The motorcycle has a great feature different from a four-wheeled vehicle in a point that the vehicle body is largely inclined in the running on a corner. For this end, the tire applied to the motorcycle is required to be excellent in the running stability during the cornering. As a technique for ensuring the running stability during the cornering, it is effective to improve the ground contacting property of the tire. From a viewpoint of the improvement of the ground contacting property, it is preferable that the deformation of not only the tread rubber for the tire but also the carcass inside the tire is easy.
As a way for facilitating the deformation of the carcass, it is effective that the deformation of a carcass ply wound around a bead core is allowed to a certain level in an axial direction of the tire. For this end, it is usually required to lower the distortion rigidity of the bead core. If it is intended to realize this requirement by decreasing the winding number of the wire, the fracture strength of the bead portion lowers. In the motorcycle tire, it is difficult to simultaneously establish the ground contacting property of the tire and the safety of the bead portion. Therefore, it is desired to develop a technique capable of sufficiently ensuring the running stability during the cornering.
On the other hand, JP-A-2002-254910 discloses a technique that the deformation of the carcass ply around the bead core can be allowed without lowering the distortion rigidity of the bead core by arranging an innerliner rubber layer enclosing the bead core along the carcass ply between the carcass ply and the bead core to render a compression ratio of the bead portion into a predetermined range.
In the tires for passenger car, so-called cable bead is applied to the bead core for reinforcing the bead portion to realize the stable running property (see JP-A-06-21100). The cable bead means a bead core having a structure that one or more sheath layers are helically wound around a single welded core wire. However, a cable bead comprising two or more sheath layers has not hitherto been used in the motorcycle tire because a region capable of arranging the bead core is narrower. An example of applying a cable bead comprising one sheath layer around the core wire to the motorcycle tire is disclosed, for example in JP-A-2002-254910.